2 * Tty buffer allocation management
5 #include <linux/types.h>
6 #include <linux/errno.h>
8 #include <linux/tty_driver.h>
9 #include <linux/tty_flip.h>
10 #include <linux/timer.h>
11 #include <linux/string.h>
12 #include <linux/slab.h>
13 #include <linux/sched.h>
14 #include <linux/init.h>
15 #include <linux/wait.h>
16 #include <linux/bitops.h>
17 #include <linux/delay.h>
18 #include <linux/module.h>
21 * tty_buffer_free_all - free buffers used by a tty
22 * @tty: tty to free from
24 * Remove all the buffers pending on a tty whether queued with data
25 * or in the free ring. Must be called when the tty is no longer in use
30 void tty_buffer_free_all(struct tty_port *port)
32 struct tty_bufhead *buf = &port->buf;
33 struct tty_buffer *thead;
35 while ((thead = buf->head) != NULL) {
36 buf->head = thead->next;
39 while ((thead = buf->free) != NULL) {
40 buf->free = thead->next;
48 * tty_buffer_alloc - allocate a tty buffer
50 * @size: desired size (characters)
52 * Allocate a new tty buffer to hold the desired number of characters.
53 * Return NULL if out of memory or the allocation would exceed the
56 * Locking: Caller must hold tty->buf.lock
59 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
63 if (port->buf.memory_used + size > 65536)
65 p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
73 p->char_buf_ptr = (char *)(p->data);
74 p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
75 port->buf.memory_used += size;
80 * tty_buffer_free - free a tty buffer
81 * @tty: tty owning the buffer
82 * @b: the buffer to free
84 * Free a tty buffer, or add it to the free list according to our
87 * Locking: Caller must hold tty->buf.lock
90 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
92 struct tty_bufhead *buf = &port->buf;
94 /* Dumb strategy for now - should keep some stats */
95 buf->memory_used -= b->size;
96 WARN_ON(buf->memory_used < 0);
107 * __tty_buffer_flush - flush full tty buffers
110 * flush all the buffers containing receive data. Caller must
111 * hold the buffer lock and must have ensured no parallel flush to
114 * Locking: Caller must hold tty->buf.lock
117 static void __tty_buffer_flush(struct tty_port *port)
119 struct tty_bufhead *buf = &port->buf;
120 struct tty_buffer *thead;
122 if (unlikely(buf->head == NULL))
124 while ((thead = buf->head->next) != NULL) {
125 tty_buffer_free(port, buf->head);
128 WARN_ON(buf->head != buf->tail);
129 buf->head->read = buf->head->commit;
133 * tty_buffer_flush - flush full tty buffers
136 * flush all the buffers containing receive data. If the buffer is
137 * being processed by flush_to_ldisc then we defer the processing
143 void tty_buffer_flush(struct tty_struct *tty)
145 struct tty_port *port = tty->port;
146 struct tty_bufhead *buf = &port->buf;
149 spin_lock_irqsave(&buf->lock, flags);
151 /* If the data is being pushed to the tty layer then we can't
152 process it here. Instead set a flag and the flush_to_ldisc
153 path will process the flush request before it exits */
154 if (test_bit(TTYP_FLUSHING, &port->iflags)) {
155 set_bit(TTYP_FLUSHPENDING, &port->iflags);
156 spin_unlock_irqrestore(&buf->lock, flags);
157 wait_event(tty->read_wait,
158 test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
161 __tty_buffer_flush(port);
162 spin_unlock_irqrestore(&buf->lock, flags);
166 * tty_buffer_find - find a free tty buffer
167 * @tty: tty owning the buffer
168 * @size: characters wanted
170 * Locate an existing suitable tty buffer or if we are lacking one then
171 * allocate a new one. We round our buffers off in 256 character chunks
172 * to get better allocation behaviour.
174 * Locking: Caller must hold tty->buf.lock
177 static struct tty_buffer *tty_buffer_find(struct tty_port *port, size_t size)
179 struct tty_buffer **tbh = &port->buf.free;
180 while ((*tbh) != NULL) {
181 struct tty_buffer *t = *tbh;
182 if (t->size >= size) {
188 port->buf.memory_used += t->size;
191 tbh = &((*tbh)->next);
193 /* Round the buffer size out */
194 size = (size + 0xFF) & ~0xFF;
195 return tty_buffer_alloc(port, size);
196 /* Should possibly check if this fails for the largest buffer we
197 have queued and recycle that ? */
200 * tty_buffer_request_room - grow tty buffer if needed
201 * @tty: tty structure
202 * @size: size desired
204 * Make at least size bytes of linear space available for the tty
205 * buffer. If we fail return the size we managed to find.
207 * Locking: Takes port->buf.lock
209 int tty_buffer_request_room(struct tty_port *port, size_t size)
211 struct tty_bufhead *buf = &port->buf;
212 struct tty_buffer *b, *n;
215 spin_lock_irqsave(&buf->lock, flags);
216 /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
217 remove this conditional if its worth it. This would be invisible
221 left = b->size - b->used;
226 /* This is the slow path - looking for new buffers to use */
227 if ((n = tty_buffer_find(port, size)) != NULL) {
237 spin_unlock_irqrestore(&buf->lock, flags);
240 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
243 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
246 * @flag: flag value for each character
249 * Queue a series of bytes to the tty buffering. All the characters
250 * passed are marked with the supplied flag. Returns the number added.
252 * Locking: Called functions may take port->buf.lock
255 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
256 const unsigned char *chars, char flag, size_t size)
260 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
261 int space = tty_buffer_request_room(port, goal);
262 struct tty_buffer *tb = port->buf.tail;
263 /* If there is no space then tb may be NULL */
264 if (unlikely(space == 0)) {
267 memcpy(tb->char_buf_ptr + tb->used, chars, space);
268 memset(tb->flag_buf_ptr + tb->used, flag, space);
272 /* There is a small chance that we need to split the data over
273 several buffers. If this is the case we must loop */
274 } while (unlikely(size > copied));
277 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
280 * tty_insert_flip_string_flags - Add characters to the tty buffer
286 * Queue a series of bytes to the tty buffering. For each character
287 * the flags array indicates the status of the character. Returns the
290 * Locking: Called functions may take port->buf.lock
293 int tty_insert_flip_string_flags(struct tty_port *port,
294 const unsigned char *chars, const char *flags, size_t size)
298 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
299 int space = tty_buffer_request_room(port, goal);
300 struct tty_buffer *tb = port->buf.tail;
301 /* If there is no space then tb may be NULL */
302 if (unlikely(space == 0)) {
305 memcpy(tb->char_buf_ptr + tb->used, chars, space);
306 memcpy(tb->flag_buf_ptr + tb->used, flags, space);
311 /* There is a small chance that we need to split the data over
312 several buffers. If this is the case we must loop */
313 } while (unlikely(size > copied));
316 EXPORT_SYMBOL(tty_insert_flip_string_flags);
319 * tty_schedule_flip - push characters to ldisc
320 * @port: tty port to push from
322 * Takes any pending buffers and transfers their ownership to the
323 * ldisc side of the queue. It then schedules those characters for
324 * processing by the line discipline.
325 * Note that this function can only be used when the low_latency flag
326 * is unset. Otherwise the workqueue won't be flushed.
328 * Locking: Takes port->buf.lock
331 void tty_schedule_flip(struct tty_port *port)
333 struct tty_bufhead *buf = &port->buf;
335 WARN_ON(port->low_latency);
337 spin_lock_irqsave(&buf->lock, flags);
338 if (buf->tail != NULL)
339 buf->tail->commit = buf->tail->used;
340 spin_unlock_irqrestore(&buf->lock, flags);
341 schedule_work(&buf->work);
343 EXPORT_SYMBOL(tty_schedule_flip);
346 * tty_prepare_flip_string - make room for characters
348 * @chars: return pointer for character write area
349 * @size: desired size
351 * Prepare a block of space in the buffer for data. Returns the length
352 * available and buffer pointer to the space which is now allocated and
353 * accounted for as ready for normal characters. This is used for drivers
354 * that need their own block copy routines into the buffer. There is no
355 * guarantee the buffer is a DMA target!
357 * Locking: May call functions taking port->buf.lock
360 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
363 int space = tty_buffer_request_room(port, size);
365 struct tty_buffer *tb = port->buf.tail;
366 *chars = tb->char_buf_ptr + tb->used;
367 memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
372 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
375 * tty_prepare_flip_string_flags - make room for characters
377 * @chars: return pointer for character write area
378 * @flags: return pointer for status flag write area
379 * @size: desired size
381 * Prepare a block of space in the buffer for data. Returns the length
382 * available and buffer pointer to the space which is now allocated and
383 * accounted for as ready for characters. This is used for drivers
384 * that need their own block copy routines into the buffer. There is no
385 * guarantee the buffer is a DMA target!
387 * Locking: May call functions taking port->buf.lock
390 int tty_prepare_flip_string_flags(struct tty_port *port,
391 unsigned char **chars, char **flags, size_t size)
393 int space = tty_buffer_request_room(port, size);
395 struct tty_buffer *tb = port->buf.tail;
396 *chars = tb->char_buf_ptr + tb->used;
397 *flags = tb->flag_buf_ptr + tb->used;
402 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
408 * @work: tty structure passed from work queue.
410 * This routine is called out of the software interrupt to flush data
411 * from the buffer chain to the line discipline.
413 * Locking: holds tty->buf.lock to guard buffer list. Drops the lock
414 * while invoking the line discipline receive_buf method. The
415 * receive_buf method is single threaded for each tty instance.
418 static void flush_to_ldisc(struct work_struct *work)
420 struct tty_port *port = container_of(work, struct tty_port, buf.work);
421 struct tty_bufhead *buf = &port->buf;
422 struct tty_struct *tty;
424 struct tty_ldisc *disc;
427 if (WARN_RATELIMIT(tty == NULL, "tty is NULL\n"))
430 disc = tty_ldisc_ref(tty);
431 if (disc == NULL) /* !TTY_LDISC */
434 spin_lock_irqsave(&buf->lock, flags);
436 if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
437 struct tty_buffer *head;
438 while ((head = buf->head) != NULL) {
441 unsigned char *flag_buf;
443 count = head->commit - head->read;
445 if (head->next == NULL)
447 buf->head = head->next;
448 tty_buffer_free(port, head);
451 /* Ldisc or user is trying to flush the buffers
452 we are feeding to the ldisc, stop feeding the
453 line discipline as we want to empty the queue */
454 if (test_bit(TTYP_FLUSHPENDING, &port->iflags))
456 if (!tty->receive_room)
458 if (count > tty->receive_room)
459 count = tty->receive_room;
460 char_buf = head->char_buf_ptr + head->read;
461 flag_buf = head->flag_buf_ptr + head->read;
463 spin_unlock_irqrestore(&buf->lock, flags);
464 disc->ops->receive_buf(tty, char_buf,
466 spin_lock_irqsave(&buf->lock, flags);
468 clear_bit(TTYP_FLUSHING, &port->iflags);
471 /* We may have a deferred request to flush the input buffer,
472 if so pull the chain under the lock and empty the queue */
473 if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
474 __tty_buffer_flush(port);
475 clear_bit(TTYP_FLUSHPENDING, &port->iflags);
476 wake_up(&tty->read_wait);
478 spin_unlock_irqrestore(&buf->lock, flags);
480 tty_ldisc_deref(disc);
487 * Push the terminal flip buffers to the line discipline.
489 * Must not be called from IRQ context.
491 void tty_flush_to_ldisc(struct tty_struct *tty)
493 if (!tty->port->low_latency)
494 flush_work(&tty->port->buf.work);
498 * tty_flip_buffer_push - terminal
499 * @port: tty port to push
501 * Queue a push of the terminal flip buffers to the line discipline. This
502 * function must not be called from IRQ context if port->low_latency is
505 * In the event of the queue being busy for flipping the work will be
506 * held off and retried later.
508 * Locking: tty buffer lock. Driver locks in low latency mode.
511 void tty_flip_buffer_push(struct tty_port *port)
513 struct tty_bufhead *buf = &port->buf;
516 spin_lock_irqsave(&buf->lock, flags);
517 if (buf->tail != NULL)
518 buf->tail->commit = buf->tail->used;
519 spin_unlock_irqrestore(&buf->lock, flags);
521 if (port->low_latency)
522 flush_to_ldisc(&buf->work);
524 schedule_work(&buf->work);
526 EXPORT_SYMBOL(tty_flip_buffer_push);
529 * tty_buffer_init - prepare a tty buffer structure
530 * @tty: tty to initialise
532 * Set up the initial state of the buffer management for a tty device.
533 * Must be called before the other tty buffer functions are used.
538 void tty_buffer_init(struct tty_port *port)
540 struct tty_bufhead *buf = &port->buf;
542 spin_lock_init(&buf->lock);
546 buf->memory_used = 0;
547 INIT_WORK(&buf->work, flush_to_ldisc);